### The Principal Value Integral symbol

This symbol (an integral sign, ‘crossed’) does not appear in any of
the fonts ordinarily available to (La)TeX users, but it can be
created by use of the following macros:

\def\Xint#1{\mathchoice
{\XXint\displaystyle\textstyle{#1}}%
{\XXint\textstyle\scriptstyle{#1}}%
{\XXint\scriptstyle\scriptscriptstyle{#1}}%
{\XXint\scriptscriptstyle\scriptscriptstyle{#1}}%
\!\int}
\def\XXint#1#2#3{{\setbox0=\hbox{$#1{#2#3}{\int}$}
\vcenter{\hbox{$#2#3$}}\kern-.5\wd0}}
\def\ddashint{\Xint=}
\def\dashint{\Xint-}

`\`

`dashint`

gives a single-dashed integral sign, `\`

`ddashint`

a
double-dashed one.

This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=prinvalint